Abstract
There are wide intra- and inter-individual variations in human chewing trajectories. This study aimed to develop the way of describing the intra-individual variations in chewing trajectories and investigate their inter-individual resemblances. The chewing trajectories of 12 healthy males who chewed gum in the right side of their mouth were recorded. Overall cycle shape was described with 123 variables consisted of three-dimensional coordinates of total 41 points at which the durations of the opening and closing phase of a chewing cycle was divided into 20 parts equally. The intra-individual variations in 200 chewing trajectories were evaluated with the principal component (PC) analysis based on a variance-covariance matrix of the variables. The variation in the trajectories that was accounted for by each PC was visualized as a reconstructed curve by using an inverse eigenvector matrix. In all subjects, the first PC was related to the changes in the gape width in each subject. Among the other PCs, which were selected by means of the scree plot analysis, two were related to the changes in the jaw-opening direction in the frontal or sagittal planes, and other one was related the width between the opening and closing trajectories. The above 4 PCs explained 74% to 87% of the variances in each of the subjects. Moreover, among the 7 PCs, which account more than 95% of the variations of the total of 2,400 chewing trajectories of all the subjects, 4 showed the similar effects on the trajectory changes as mentioned above. Inter-individual resemblances were present among the intra-individual changes in the chewing trajectories. This would suggest that the subjects utilized identical strategies in controlling chewing trajectories.
